Qi Faren, chief designer of the Shenzhou spacecraft, told China Daily that the core module will weigh about 20 tons and incorporate a connecting part that has multiple berthing mechanisms so that it can link with modules such as a lifeboat or cargo spaceship.

Now in the second stage of its manned space program, China needs to master four technologies to launch the space station in the third and final stages, he said.

Astronauts carried out extravehicular activity during the Shenzhou VII mission last year and scientists are now working on the challenge of space docking, Qi said.

"The Tiangong I, or Heavenly Palace I, which is scheduled for launch before 2011, is the platform to test the space docking technology," he said.

"In its one- to two-year lifespan, Tiangong I, which weighs 8.5 tons, will be the object that Shenzhou VIII, Shenzhou IX and Shenzhou X will dock with in order to test the technology," he said.

According to the plan, Shenzhou VIII is an unmanned spaceship that will try to dock Tiangong I in 2011, if preparations go smoothly, he said.

If that mission is a success, manned spaceships will be launched to dock with the Tiangong I, he said.

"Then we will improve Tiangong I and develop the space laboratory," he said.

The space laboratory will operate unattended in the long term but will be taken care of by astronauts in the short term, so China also has to solve the supply problem, Qi said.

"We will launch a cargo spaceship that will send several tons of supplies, including water, food, air and other items to the space laboratory," he said.

At the moment, the Shenzhou spaceships can carry only 300 kg of supplies when three astronauts are aboard, he said.

Scientists will also have to conquer the problem of recycling air and water in the space laboratory, he said.

When all these problems have been solved, China will be ready to launch its space station atop a CZ-5 rocket from the new launch center in Hainan province, he said.

The Xinhua News Agency reported last week that a prototype of Tiangong I is almost ready.